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Water Treatment for NYC
Croton Schematic
NYC Filtration Plant for Delaware and Catskill Systems
Filtration avoidance criteria Alternatives to Filtration Where should the plant(s) be located?
Multiple plants or one plant?Treatment steps at different locations?
Design flow Treatment scheme Backwash water
Safe Drinking Water Act Turbidity Loophole
At no time can turbidity (cloudiness of water) go above 5 nephelolometric turbidity units (NTU)
Systems that filter must ensure that the turbidity never exceed 1 NTU, and must not exceed 0.3 NTU in 95% of daily samples in any month
NYC DEP Data Interpretation
As of 2001 NYC only reports monthly average turbidity
“The MCL for turbidity is the monthly average rounded off to the nearest whole number”
“Data presented are range and averages of monthly averages”
Average turbidity (NTU)
Croton Delaware Catskill
2001 1.4 1.1
2002 1.1 1
141.71 Criteria for Avoiding filtration
The turbidity level cannot exceed 5 NTU (measured as specified in § 141.74 (a)(4) and (b)(2)) in representative samples of the source water immediately prior to the first or only point of disinfectant application unless: (i) the State determines that any such event was caused by circumstances that were unusual and unpredictable; and (ii) as a result of any such event, there have not been more than two events in the past 12 months the system served water to the public, or more than five events in the past 120 months the system served water to the public, in which the turbidity level exceeded 5 NTU. An ‘‘event’’ is a series of consecutive days during which at least one turbidity measurement each day exceeds 5 NTU.
Limited Alternative To Filtration
States may allow unfiltered water systems with surface water sources to use treatment other than filtration
In order to qualify for alternative treatment, a water system must have an __________, ____________ watershed in consolidated ownership and have control over access to and activities in the watershed
The alternative treatment must ensure _________ removal or inactivation efficiencies of pathogenic organisms than would be achieved by the combination of filtration and chlorine disinfection required by section 1412 (b)(7)(C). [1412(b)(7)(C)] Sec. 106
uninhabited undeveloped
greater
§ 141.71 Criteria for Avoiding Filtration
The public water system must demonstrate through ownership and/or written agreements with landowners within the watershed that it can control all human activities which may have an adverse impact on the micro-biological quality of the source water. The public water system must submit an annual report to the State that identifies any special concerns about the watershed and how they are being handled; describes activities in the watershed that affect water quality; and projects what adverse activities are expected to occur in the future and describes how the public water system expects to address them.
Should NYC have to Filter?
Pro Con
Croton Plant
The construction costs of the water filtration plant, with a design capacity of 290 million gallons per day (mgd), and the related facilities, is estimated at $660 million.
Annual operations and maintenance costs are projected to be $11 million.
The plant will use state-of-the-art disinfection and filtration processes including dissolved air flotation for the removal of solids, ozonation for primary disinfection, and biologically active carbon filtration.
3 3
33
$660,000,000 $5212.7
$5283 4.3 !
millionm s m s
millionm s billion
m s
=
× =To treat Delaware Catskill water
Croton Treatment Scheme
Croton Plant
Where Should Plant(s) Be Located for Catskill/Delaware?
______________________________________________________________________
_________________________________________________________________________________________________________
Between last watershed reservoir (Kensico) anddistribution reservoir (Hillview)
Near tunnel
On hydraulic grade line! (No pumps)
Commercial/Industrial area (not residential)
Design Flow for Water Treatment Plant
Max day ever was 94 m3/s in 1975Future growth?Conservation?
Croton system is separateProposed filtration plant for 12.7 m3/sAbility to shut down Croton system?
Catskill/Delaware designed for 83 m3/s
Maximum Daily Flow
0.010.020.030.040.050.060.070.080.090.0
1978
1980
1982
1984
1986
1988
1990
1992
1994
year
Max
imum
dai
ly d
eman
d (m
3 /s)
Catskill/Delaware
Croton
Treatment Plant Options for NYC
NYC’s water is high quality (<2 NTU)Low particle concentration means that
___________ ______ aren’t necessaryThree options for WTP with high quality
surface watersDirect FiltrationContact FiltrationUltraviolet disinfection (selected by NYC)
sedimentation basins
Direct Filtration
Screening
Rapid Mix
Flocculation
Filtration
Disinfection
Storage
Distribution
Raw water
AlumPolymers
Cl2
sludge sludge
Contact Filtration
Screening
Rapid Mix
Filtration
Disinfection
Storage
Distribution
Raw water
AlumPolymers
Cl2
sludge sludge
UV Disinfection
Kills pathogensDoes not reduce turbidityMay be approved as an alternative to
filtration for NYC Catskill/Delaware water supply
Costs much less than a filtration plant
Size of Major Unit Processes
Unit Process Parameter Range
Flocculation 10-30 min
Sedimentation Q/As 0.67 m/hr
Filtration Va 2.5 - 37 m/hr
Los Angeles - _______
37 m/hr
Backwash Requirements
U FB B
TTotal filter bed areaotal filter bed area
Useable production (or area)
Production used for backwash
Filter beds off line to be backwashed
AT = AU + AFB + AB
Area of Filter Beds in Useable Production (U)
Plant Design Flow83 m3/s
Area required without backwash (Va = 25 m/hr)
Backwash requirements?10 minutes at 50 m/hr once every 12 hours assume 30 minute downtime for backwashThe useable filter bed area must be increased by 5 – 10%
to meet backwash requirements
23
U m 11,952
s 3600hr
hrm 25
/sm 83
VQ
A 36.4 ha siteha=10,000 m2
Backwash Water Disposal Options
Backwash water productionApproximately 3% of useable production!Often not recycled because of potential concentration
of pathogensWill be recycled at the Croton filtration plant
Solids productionparticles present in raw water (0.1-10 mg/L) coagulant (5 - 50 mg/L)
Disposal options
Area of Flocculation Tanks
Hydraulic retention time of 10-30 minutesLos Angeles uses 8 minutes
Typical depth of 5 metersArea required for flocculation will be
similar to that required for filtrationContact filtration would eliminate the need
for flocculation tanks
Summary
NYC is designing an ultraviolet disinfection plant (with 2009 target for operation)
The WTP will be constructed somewhere between Kensico and Hillview Reservoirs
The WTP will be designed to handle recent peak daily flows
Supply Aqueducts and Tunnels
Catskill Aqueduct
Delaware Aqueduct
East Delaware tunnel
West Delaware tunnel
Shandaken Tunnel
Neversink Tunnel
Kensico to Hillview
CatskillAqueduct
DelawareAqueduct
Possible Water Treatment Plant Site
Kensico
1 km
90 acre site36.4 haha=10,000 m2
Close to Catskill and Delaware Aqueducts
Possible Water Treatment Plant Site